In the above-mentioned JP-A-2000-290356, no detail is disclosed with respect to the starting material 1,4-cyclohexanedicarboxylic acid. However, a polyester obtained by using 1,4-cyclohexanedicarboxylic acid which is commonly used as the material for a polyester of this type, has been found to still have room for further improvement with respect to the transparency and color tint.
The present invention has been made in view of the above-described circumstances, and it is an object of the present invention to have the transparency improved in a polyester resin wherein 1,4-cyclohexanedicarboxylic acid is the main dicarboxylic acid component and preferably to provide a polyester resin having the yellowish tint further reduced. Further, it is an object of the present invention to provide a resin composition containing such a polyester resin, and a hollow container, sheet and film obtained by using such a polyester resin or a resin composition.
As a result of an extensive study, the present inventors have found that in a polyester resin wherein 1,4-cyclohexanedicarboxylic acid is the main dicarboxylic acid component, the light transmittance of the starting material monomer for the polyester is influential over the transparency and yellowing of the resin, and a polyester obtained by using 1,4-cyclohexanedicarboxylic acid having a specific light transmittance, has excellent transparency and color as compared with a polyester obtained by using conventional 1,4-cyclohexanedicarboxylic acid. The present invention has been accomplished on the basis of these discoveries.
Namely, the present invention provides a polyester resin which is an alicyclic polyester comprising dicarboxylic acid units and diol units, characterized in that (1) the dicarboxylic acid units are composed mainly of 1,4-cyclohexanedicarboxylic acid units, (2) the diol units are composed mainly of 1,4-cyclohexanedimethanol units, (3) the ratio of alkyl ester terminals to all terminals of the polyester is at most 5 mol %, and (4) the light transmittance of a molded plate of the resin having a thickness of 2 mm is at least 87%.
The present invention also provides a polyester resin which is a polyester resin obtained by reacting a dicarboxylic acid component containing 1,4-cyclohexanedicarboxylic acid as the main component, with a diol component, characterized in that (1) 1,4-cyclohexanedicarboxylic acid units constituting the polyester comprise trans-1,4-cyclohexanedicarboxylic acid units and/or cis-1,4-cyclohexanedicarboxylic acid units, (2) the ratio of trans-1,4-cyclohexanedicarboxylic acid units to the total 1,4-cyclohexanedicarboxylic acid units, is at least 85 mol %, and (3) the light transmittance of a molded plate of the resin having a thickness of 2 mm is at least 87%.
Such a polyester resin of the present invention preferably has a Yellowness Index (YI) of at most 18.
Further, the present invention provides a resin composition comprising the above polyester resin, and a thermoplastic resin and/or elastomer, and a hollow molded container, sheet or film obtained by using such a polyester resin or resin composition.